Polar chemical compounds, because of their water solubility, cannot be treated with the foam types commonly used to combat spills and fires of water immiscible organic materials. Special foams have been formulated for use on polar compounds, the most widely used containing a polysaccharide. The polysaccharide gels on contact with the polar compound forming a floating layer that separates the foam from the polar liquid and allows a foam blanket to build for fire extinguishment and/or vapor suppression.
Not all polysaccharides exhibit this gelling property, but those that do are also characterized by pseudo water solubility. That is, when mixed with water, they absorb it and disperse uniformly but do not fully dissolve to form a true solution (although they are ordinarily referred to as solutions and are so referred to herein). In most cases the colloidal dispersion is stable, but outside factors can destabilize and cause settling of the polysaccharide.
One category of materials which can cause destabilization is surface active agents. Since a surface active agent is necessary to produce foams, foam chemistries involving polysaccharides can be difficult to formulate. Current formulations use the technique of thickening the foam concentrate formulation such that settling is prevented. Normally, highly viscous materials cannot be handled by the proportioning devices in common use by the fire services. Some currently used foam chemistries are thixotropic, however, and their inherent ability to act as a lower viscosity fluid in high shear flow permits their use with many existing proportioning devices. See, for example, U.S. Pat. Nos. 4,060,132, 4,060,489, 4,149,599 and 4,387,032. Some proportioning arrangements, such as gravity flow to a metering or similar pump, can have difficulties with thixotropic concentrates. Also, at cold temperatures the viscosity of thixotropic concentrates increases to the point that all proportioning devices experience decreased performance. Since there is a critical minimum of foam concentrate in water for foam generation and/or effective fire suppression, a reduction in proportioning rate could be harmful.